Thursday, December 8, 2022

What is weld deposition efficiency?

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When we think in terms of weld deposition efficiency we refer to the one that occurs in areas of mass production, and not the occasional one that we can make in our garage.

Imagine that you have to weld not one but a thousand TV mounts; well, when it comes to mass production, variables come into play that are not normally considered for artisanal manufacturing.

One of these variables is the deposition of metal in the weld, and the competitiveness of the finished product depends on it, since the amount of electrode used —and especially what proportion of the electrode is used— will depend on the economic success of our undertaking.

Increase efficiency in weld deposition

There are three engineering factors to take into account when planning welding: the preparation of the materials to be welded, the welding technique to be used and the welding parameters to be implemented.

All three variables are intimately related, and must be factored into the cost-benefit equation right from the drawing board.

Preparation of materials for welding

How will you weld the pieces together? Think about the cost-benefit ratio of each joining technique. Some profiles allow extremely robust joints to be achieved, but require more filler material; others, on the contrary, are more fragile.

Section of a weld with X or double V profile.

It is known that the best compromise between quality and resistance occurs in X joints, or double V, where the filler material required is less than in V or T joints; the only drawback is that it is necessary to weld on both sides, so it is also necessary to think about the costs of preheating.

Another important issue to keep in mind is that both surfaces to be joined must be clean of grease and other impurities, and where possible, sandblasted, polished and free of any grease or moisture on their surfaces.

welding technique

For modest production, with joints that do not compromise structural integrity, or in small complementary welds, use can be made of covered electrode arc welding.

For important joints it is already necessary to think about techniques such as MIG or TIG, in which the puddle of filler metal is more controllable and the proportion of discard in the electrode is much smaller. Remember that, in the best of cases, it is only possible to use 67% of the material of a covered electrode for SMAW welding.

In the case of autogenous welding —either by arc or by oxyacetylene flame— it is possible to say that the weld deposition efficiency it is total, since there is no contribution of material; The problem is that this technique is rarely possible, because one of the requirements is that the pieces to be joined have the same metallographic composition.

Welding parameters

Efficiency in weld deposition

Efficiency in weld deposition

The parameters used for welding greatly influence the weld deposition efficiency. Let’s remember that with arc welding, we have three factors to consider: current, electrode feed (MIG) and wire diameter (MIG). Of these three parameters, the most important in general is the current, or the heat of welding.

If the current is excessive, too wide a weld bead will be formed, and there is a risk of excessive penetration. On the other hand, if the current is very poor, the bead will be narrow, and there will be little penetration, making the weld brittle.

Difference between a good weld and a bad one

Welding parameters and their influence on the seam and quality.

When welding using the TIG technique, if the current is very high, tungsten inclusions will begin to form in the weld bead, something that affects both the quality and durability of the electrode. In the MIG technique, spatter occurs or the wire burning, backing up to the torch and often causing melt damage there.

The presence of the correct gas not only prevents weld corrosion, but also helps increase weld deposition efficiency by allowing a cleaner flow of filler material.

Modern welding equipment (IGBT, inverters) allow automatic control of the welding parameters, delegating that control to a computer that constantly monitors the feedback, correcting the power, frequency and output voltage, with which it is only necessary to establish the correct preparation of the equipment before starting the operation, calculating the feed and the diameter of the wire (in MIG welding), and the current or voltage plus the polarity in either case.

Some tips to increase efficiency in weld deposition

  • If you don’t have a table with approximate parameters for the weld you’re trying to make, do trial and error on a piece of scrap. In this way, you will be able to verify the optimal parameters and dump them over time to a paper file or to a database or spreadsheet on your computer or telephone, for later consultation.
  • If you are going to work in production, use TIG or MIG techniques; avoid the use of manual stick welding, as of all the techniques it is the least efficient in terms of deposition (and the least consistent in terms of results).
  • In MIG welding, every 0.25mm of material thickness requires approximately 10A of current.
  • The diameter of the wire (MIG) can be chosen roughly according to the necessary current; up to 130 A choose diameter 0.6 mm; up to 145A, 0.75mm; up to 180A, 0.9mm; up to 250 A, 1.15 mm.
  • Always use shielding gas.

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